The present invention relates to coating compositions for application to metallic surfaces to impart corrosion resistance thereto, such as resistance to oxidation upon prolonged exposure to salt water, salt air and/or moisture in general.
A wide variety of corrosion-resistant coating compositions are known for application to metallic surfaces. Some such compositions are effective but are carcinogenic and have disadvantageous toxic properties which present a danger to persons exposed thereto, and to the environment, and therefore preclude their use for many applications. Metal chromate, permanganate, lead and, in general, heavy metal inhibitor compositions fall within this category.
Many known corrosion-inhibitor compositions, including chromates, require the use of strong acids such as sulfuric, hydrochloric, hydrofluoric or hydriodic acid, and organic solvents such as aromatic solvents and diluents which are ozone-depleting agents and/or are dangerous to the health and/or present environmental and toxic waste disposal problems. Such compositions include a wide variety of silicone polymer compositions, including those disclosed in U.S. Pat. No. 3,166,527. Such compositions, coated onto the metal workpieces and dried or cured by evaporation of the organic solvents, are only as effective as their ability to form a lasting adhesion to the metal surface.
Other silane/siloxane corrosion resisting compositions soluble in water/alcohol vehicles are known, such as disclosed in U.S. Pat. No. 3,234,144 for use in automobile coolant systems. Such compositions contain low molecular weight dimer and trimer compounds of organosilicon which are not crosslinkable during use, do not form integral, cured high molecular weight polysiloxanes, and/or require highly active organometallic catalysts.